Method for producing pyridine derivatives

ABSTRACT

A pyridine alcohol derivative represented by General Formula III                    
     (where A represents a divalent organic group which may contain one to three oxygen atoms, nitrogen atoms and/or sulfur atoms, wherein A may form a 5-, 6-, 7-, or 8-membered ring together with two bonded carbon atoms, where said ring may form a condensed ring with one or more additional rings; R 5  represents a hydrogen atom, —CHR 1 R 2 , or an alkenyl group, an aryl group or an aralkyl group which may be substituted; R 1  and R 2  each independently represent a hydrogen atom or a hydrocarbon group which may be substituted; and R 6  represents a hydrogen atom, an alkyl group, an alkenyl group, an aryl group or an aralkyl group which may be substituted), is produced by: 
     reacting a pyridine ester derivative represented by General Formula I-1                    
      (where Z 1  represents —COX; X represents an alkoxyl group, an alkenyloxy group, an aryloxy group or an aralkyloxy group which may be substituted; and A is the same as above) with a reducing agent, an alkylating agent, an alkenylating agent, an arylating agent or an aralkylating agent to obtain a pyridine carbonyl derivative represented by General Formula II                    
      (where A and R 5  are the same as above); and 
     reacting the resulting pyridine carbonyl derivative with a reducing agent, an alkylating agent, an alkenylating agent, an arylating agent or an aralkylating agent to obtain the pyridine alcohol derivative of the General Formula III.

This application is a Division of application Ser. No. 09/175,958 filedon Oct. 21, 1998, now U.S. Pat. No. 6,111,111.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods for producing pyridinederivatives, and to intermediates in the synthesis thereof. The pyridinederivatives produced by the present invention are useful asintermediates in the synthesis of compounds having a pyridine skeletonin the molecule, such as furopyridine derivatives having antiviralactivity (see WO 96/35678).

2. Description of the Related Art

Several methods have been disclosed in the past as methods for thesynthesis of condensed pyridines such as furopyridines (seeHeterocycles, 45(5) (1997), p. 975), but the only known methods forproducing 5-substituted furo[2,3-c]pyridines which can be converted tothe aforementioned furopyridine derivatives having antiviral activityare methods in which synthesis is achieved through multiple stages using2-chloro-3-hydroxypyridine as the starting material (see WO 96/35678),and methods in which furfural oxime as the starting material is madeinto 5-substituted furo[2,3-c]pyridine-N-oxide as a result of ringformation by the Aza Diels-Alder reaction and subsequent dehydrogenation(see Tetrahedron Lett., 32, 3199(1991)).

Problems in the former of the aforementioned methods, however, are thelarge number of steps as well as the expensive starting materials andreaction agents, while the latter method needs expensive dehydrogenatingagents such as 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and needsthe reduction of the pyridine oxide to pyridine, and hence both methodscannot be considered to be industrially useful.

SUMMARY OF THE INVENTION

An object of the present invention is to provide methods in whichpyridine derivatives, that allow condensed pyridines such asfuropyridine derivatives to be readily produced, can be manufacturedwith good yields in an industrially useful manner under moderateconditions.

Another object of the present invention is to provide a syntheticintermediate and its method of production giving an industrially usefulmethod for producing the aforementioned pyridine derivatives.

The aforementioned objects have been achieved in the following presentinvention.

The present invention provides a method for producing a pyridine alcoholderivative represented by General Formula III

(where A represents a divalent organic group which may contain one tothree oxygen atoms, nitrogen atoms and/or sulfur atoms, wherein A mayform a 5-, 6-, 7-, or 8-membered ring together with two bonded carbonatoms, and said ring may form a condensed ring with one or moreadditional rings; R⁵ represents a hydrogen atom, —CHR¹R², or an alkenylgroup, an aryl group or an aralkyl group which may be substituted; R¹and R² each independently represent a hydrogen atom or a hydrocarbongroup which may be substituted; and R⁶ represents a hydrogen atom, analkyl group, an alkenyl group, an aryl group or an aralkyl group whichmay be substituted), wherein the method comprises:

reacting a pyridine ester derivative represented by General Formula I-1

 (where Z¹ represents —COX; X represents an alkoxyl group, an alkenyloxygroup, an aryloxy group or an aralkyloxy group which may be substituted;and A is the same as above) with a reducing agent, an alkylating agent,an alkenylating agent, an arylating agent or an aralkylating agent toobtain a pyridine carbonyl derivative represented by General Formula II

 (where A and R⁵ are the same as above); and

reacting the resulting pyridine carbonyl derivative represented byGeneral Formula II with a reducing agent, an alkylating agent, analkenylating agent, an arylating agent or an aralkylating agent toobtain the pyridine alcohol derivative of the General Formula III.

The present invention also provides a method for producing a pyridinealcohol derivative represented by General Formula III, wherein themethod comprises:

reacting a pyridine carbonyl derivative represented by General FormulaII with a reducing agent, an alkylating agent, an alkenylating agent, anarylating agent or an aralkylating agent to obtain the pyridine alcoholderivative of the General Formula III.

The present invention further provides a pyridine carbonyl derivativerepresented by General Formula II-1

(where R⁵ represents a hydrogen atom, —CHR¹R², or an alkenyl group, anaryl group or an aralkyl group which may be substituted; R¹ and R² eachindependently represent a hydrogen atom or a hydrocarbon group which maybe substituted; Q represents a divalent group selected from —ND—, —O—,and —S—; and D represents a hydrogen atom or a hydrocarbon group whichmay be substituted).

The present invention still further provides a method for producing apyridine carbonyl derivative represented by General Formula II, whereinthe method comprises:

reacting a pyridine ester derivative represented by General Formula I-1with a reducing agent, an alkylating agent, an alkenylating agent, anarylating agent or an aralkylating agent.

The present invention also provides a method for producing a pyridinealcohol derivative represented by General Formula III, wherein themethod comprises:

reacting a pyridine ester derivative represented by General Formula I-1in the presence of a base with an ester compound represented by GeneralFormula IV

R¹R²CHCO₂R³  (IV)

 (where R¹ and R² are the same as above; and R³ represents a hydrocarbongroup which may be substituted) to obtain a pyridine β-ketoesterderivative represented by General Formula V

 (where R¹, R², and A are the same as above; and R⁴ is a hydrocarbongroup which may be substituted); and

hydrolyzing and decarboxylating the resulting pyridine β-ketoesterderivative represented by General Formula V to obtain the pyridinecarbonyl derivative represented by General Formula II; and

reacting the pyridine carbonyl derivative represented by General FormulaII with a reducing agent, an alkylating agent, an alkenylating agent, anarylating agent or an aralkylating agent to obtain the pyridine alcoholderivative represented by General Formula III.

The present invention further provides a method for producing a pyridineβ-ketoester derivative represented by General Formula V, wherein themethod comprises:

reacting a pyridine ester derivative represented by General Formula I-1with in the presence of a base with an ester compound represented byGeneral Formula IV to obtain the pyridine β-ketoester derivativerepresented by General Formula V.

The present invention still further provides a pyridine β-ketoesterderivative represented by General Formula V-1

(where R¹ and R² each independently represent a hydrogen atom or ahydrocarbon group which may be substituted; R⁴ represents a hydrocarbongroup which may be substituted; Q represents a divalent group selectedfrom —ND—, —O—, and —S—; and D represents a hydrogen atom or ahydrocarbon group which may be substituted).

The present invention also provides a method for producing a pyridinecarbonyl derivative represented by General Formula II, wherein themethod comprises:

hydrolyzing and decarboxylating a pyridine β-ketoester derivativerepresented by General Formula V to obtain the pyridine carbonylderivative represented by General Formula II.

The present invention also provides a pyridine ester derivativerepresented by General Formula I-1′

(where Z¹ represents —COX; and X represents an alkoxyl group, alkenyloxygroup, aryloxy group or aralkyloxy group which may be substituted).

The present invention also provides a sulfonylpyridine derivativerepresented by General Formula I-2

(where Z² represents an organic sulfonyl group represented by —SO₂R⁹;R⁹represents an organic group; and A represents a divalent organic groupwhich may contain one to three oxygen atoms, nitrogen atoms and/orsulfur atoms, wherein A may form a 5-, 6-, 7-, or 8-membered ringtogether with two bonded carbon atoms, and said ring may form acondensed ring with one or more additional rings).

The present invention also provides a method for producing a pyridinederivative represented by General Formula I

(where n of Z^(n) is 1 or 2; Z¹ represents —COX; X represents an alkoxylgroup, an alkenyloxy group, an aryloxy group or an aralkyloxy groupwhich may be substituted; Z² represents an organic sulfonyl grouprepresented by the formula, —SO₂R⁹; R⁹ is an organic group; and Arepresents a divalent organic group which may contain one to threeoxygen atoms, nitrogen atoms and/or sulfur atoms, wherein A may and forma 5-, 6-, 7-, or 8-membered ring together with two bonded carbon atoms,and said ring may form a condensed ring with one or more additionalrings), wherein the method comprises:

reacting an imine derivative represented by General Formula VI

 (where R⁷ is an alkyl group, an alkenyl group, an aryl group or anaralkyl group which may be substituted; and A is the same as above) witha carbonylating agent represented by General Formula VII

 (where R⁸ is a hydrogen atom, an alkyl group, an alkenyl group, an arylgroup, an aralkyl group, an alkoxyl group, an alkenyloxy group, anaryloxy group, an aralkyloxy group or an amino group which may besubstituted; and Y represents a leaving group) and a nitrile derivativerepresented by General Formula VIII

Z^(n)CN  (VII)

 (where Z_(n) is the same as above) to obtain the pyridine derivativerepresented by General Formula I.

The imine derivative represented by General Formula VI may preferably beobtainable by a method comprises:

reacting an aldehyde derivative represented by the General Formula IX

 (where A is the same as above) with a primary amine represented by theGeneral Formula X

R⁷NH₂  (X)

 (where R⁷ is the same as above) to obtain the imine derivativerepresented by General Formula VI.

These and other objects, features and advantages of the presentinvention are described in or will become apparent from the followingdetailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be explained in more detail by referring tothe following Reaction Scheme.

First, the substituents referred to in the General Formulas in theReaction Scheme are explained below.

Specific examples of rings formed by A together with two bonded carbonatoms in the aforementioned general formula include 5-membered ringssuch as a dihydrofuran ring, a furan ring, a pyrrole ring, a pyrrolinering, a dehydrodioxolane ring, a pyrazole ring, a pyrazoline ring, animidazole ring, an oxazole ring, an isooxazole ring, a thiazole ring, anoxadiazole ring, and a triazole ring; 6-membered rings such as a pyranring, a dihydropyran ring, a pyridine ring, a dihydropyridine ring , atetrahydropyridine ring, a dehydrodioxane ring, a dehydromorpholinering, a pyridazine ring, a dihydropyridazine ring, a pyrimidine ring, adihydropyrimidine ring, a tetrahydropyrimidine ring, a pyrazine ring,and a dihydropyrazine ring; 7-membered rings such as a thiazepine ringand various aza, oxa and thia substituted derivatives of a cycloheptenering, a cycloheptadiene ring and a cycloheptatriene ring; and 8-memberedrings such as various aza, oxa or thia substituted derivatives of acyclohetene ring, a cycloheptadiene ring and a cyclooctatetraene ring.

Specific examples of condensed rings in cases where the ring formed by Atogether with two bonded carbon atoms forms a condensed ring with one ormore other rings include a benzofuran ring, an isobenzofuran ring, achromene ring, an indolizine ring, an indole ring, an isoindole ring, aquinolizine ring, an indazole ring, an isoquinoline ring, a phthalazinering, a naphthylizine ring, a quinoxaline ring, a benzothiophene ringand their hydrogenated forms. Any of the above rings may be substituted.

Examples of alkoxyl groups represented by X or R⁸ include linear orbranched alkoxyl groups such as methoxy, ethoxy, propoxy, isopropoxy,butoxy, hexyloxy and octyloxy; and cycloalkyloxy groups such ascyclopropyloxy, cyclopentyloxy, and cyclohexyloxy. These alkoxyl groupsand cycloalkyloxy groups may be substituted, where examples of suchsubstituents include halogen atoms such as chlorine, bromine, iodine andfluorine; alkoxyl groups such as methoxy, ethoxy, propoxy and butoxy;hydroxyl group; nitro group; and aryl groups such as phenyl,p-methoxyphenyl and p-chlorophenyl.

Examples of alkenyloxy groups represented by X or R⁸ includepropenyloxy, butenyloxy and octenyloxy; examples of aryloxy groupsinclude the phenyloxy; and examples of aralkyloxy groups include thebenzyloxy. These alkenyloxy, aryloxy and aralkyloxy groups may besubstituted, where examples of such substituents include halogen atomssuch as chlorine, bromine, iodine and fluorine; alkoxyl groups such asmethoxy, ethoxy, propoxy and butoxy; hydroxyl group; alkyl groups suchas methyl, ethyl, propyl and butyl; tri-substituted silyloxy groups suchas tert-butyldimethylsilyloxy and tert-butyldiphenylsilyloxy; nitrogroup; and aryl groups such as phenyl, p-methoxyphenyl andp-chlorophenyl.

Examples of organic groups represented by R⁹ include alkyl groups suchas methyl, ethyl, propyl, ter-butyl, octyl and dodecyl; aryl groups suchas phenyl, tolyl, chlorophenyl, nitrophenyl and naphthyl; and aralkylgroups such as benzyl and nitrobenzyl.

Examples of hydrocarbon groups represented by R¹, R², R³, R⁴ and Dinclude alkyl, alkenyl, aryl and aralkyl groups. Examples of alkylgroups include linear or branched alkyl groups such as methyl, ethyl,propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl,isopentyl, neopentyl, hexyl, heptyl and octyl; and cycloalkyl groupssuch as cyclopropyl, cyclopentyl and cyclohexyl. These alkyl groups maybe substituted, where examples of such substituents include halogenatoms such as chlorine, bromine, iodine and fluorine; alkoxyl groupssuch as methoxy, ethoxy, propoxy and butoxy; hydroxyl group;tri-substituted silyloxy groups such as tert-butyldimethylsilyloxy andtert-butyldiphenylsilyloxy; nitro group; and aryl groups such as phenyl,p-methoxyphenyl and p-chlorophenyl.

Examples of alkenyl groups include vinyl, propenyl, butenyl and octenyl;examples of aryl groups include phenyl; and examples of aralkyl groupsinclude benzyl. These alkenyl, aryl, and aralkyl groups may besubstituted, where examples of such substituents include halogen atomssuch as chlorine, bromine, iodine and fluorine; alkoxyl groups such asmethoxy, ethoxy, propoxy and butoxy; hydroxyl group; alkyl groups suchas methyl, ethyl, propyl and butyl; tri-substituted silyloxy groups suchas tert-butyldimethylsilyloxy and tert-butyldiphenylsilyloxy; nitrogroup; and aryl groups such as phenyl, p-methoxyphenyl andp-chlorophenyl.

Examples of alkyl groups represented by R⁵, R⁶, R⁷ and R⁸ include linearor branched alkyl groups such as methyl, ethyl, propyl, isopropyl,butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl,hexyl, heptyl and octyl; and cycloalkyl groups such as cyclopropyl,cyclobutyl, cyclopentyl and cyclohexyl.

These alkyl groups may be substituted, where examples of suchsubstituents include halogen atoms such as chlorine, bromine, iodine andfluorine; hydroxyl group; alkoxyl groups such as methoxy, ethoxy,propoxy and butoxy; tri-substituted silyloxy groups such astert-butyldimethylsilyloxy and tert-butyldiphenylsilyloxy; nitro group;and aryl groups such as phenyl, p-methoxyphenyl and p-chlorophenyl.

Examples of alkenyl groups represented by R⁵, R⁶, R⁷ and R⁸ includevinyl, propenyl, butenyl and octenyl; examples of aryl groups includephenyl and naphthyl; and examples of aralkyl groups include benzyl.These alkenyl, aryl and aralkyl groups may be substituted, whereexamples of such substituents include halogen atoms such as chlorine,bromine, iodine and fluorine; hydroxyl group; alkyl groups such asmethyl, ethyl, propyl and butyl; alkoxyl groups such as methoxy, ethoxy,propoxy and butoxy; tri-substituted silyloxy groups such astert-butyldimethylsilyloxy and tert-butyldiphenylsilyloxy; nitro group;and aryl groups such as phenyl, p-methoxyphenyl, and p-chlorophenyl.

Examples of substitutable amino groups represented by R⁸ include C1 toC8 linear or branched amino groups such as amino, dimethylamino,diethylamino, dipropylamino, diisopropylamino, dibutylamino,dihexylamino and dioctylamino.

These amino groups may be substituted by halogen atoms such as chlorine,bromine, iodine or fluorine; hydroxyl group; alkoxyl groups such asmethoxy, ethoxy, propoxy or butoxy; tri-substituted silyloxy groups suchas tert-butyldimethylsilyloxy and tert-butyldiphenylsilyloxy; nitrogroup; and phenyl, p-methoxyphenyl and p-chlorophenyl groups.

Examples of leaving groups represented by Y include halogen atoms suchas chlorine, bromine and iodine, and acyloxy groups such as acetoxy,propionyloxy, butyryloxy and valeryloxy.

Production method of the present invention is described in each step indetail below.

Step (a): Step for producing an imine derivative VI by subjecting analdehyde derivative IX and a primary amine X to dehydrationcondensation.

This conversion can be carried out in the same way as in methodscommonly used to obtain an imine compound from an aldehyde and a primaryamine. For example, the aldehyde derivative IX and the primary amine Xare mixed in the presence or absence of a solvent and in the presence orabsence of a dehydrating agent. Suitable solvents are those which giveno undesired effect on the reaction, including aliphatic hydrocarbonsolvents such as pentane, hexane, heptane and ligroin; aromatichydrocarbon solvents such as benzene, toluene, xylene and chlorobenzene;ether solvents such as diethyl ether, tetrahydrofuran and dioxane;alcohol solvents such as methanol and ethanol; ester solvents such asmethyl acetate, ethyl acetate and butyl acetate; or a mixture thereof.Suitable dehydrating agents include silica gel, molecular sieves,alumina, sodium sulfate, magnesium sulfate, copper sulfate, sodiumhydroxide, or potassium hydroxide. The reaction can also be carried outin an azeotropic solvent with water while removing water by azeotropicdehydration.

Examples of the primary amines X include methylamine, ethylamine,propylamine, n-buthylamine, n-hexylamine, n-octylamine, aniline,p-chloroaniline, p-methoxyaniline, p-methylaniline and p-nitroaniline.

The resulting imine derivative VI is isolated and purified from thereaction mixture in the usual manner which commonly used in theisolation and purification of organic compounds. For example, the iminederivatives VI can be obtained by separating insoluble materialcontained in the reaction mixture by filtration, concentrating thefiltrate and then purifing the residue by recrystallization,chromatography, or the like. The crude product can also be used withoutpurification as such in subsequent reactions. When the imine derivativeVI is precipitated from the reaction mixture, it is filtered, purifiedby recrystallization if necessary, and then can be used in thesubsequent reaction.

Step (b): Step for producing a pyridine derivative I by reacting animine derivative VI with a carbonylating agent VII and a nitrile VIII.

Examples of carbonylating agents VII include carboxylic anhydrides suchas acetic anhydride, propionic anhydride, butyric anhydride, valericanhydride and trifluoroacetic anhydride; carboxylic acid halides such asacetyl chloride, acetyl bromide, propionyl chloride, propionyl bromide,butyryl chloride, isobutyryl chloride, valeryl chloride, isovalerylchloride, pivaloyl chloride, benzoyl chloride and benzoyl bromide;halogenoformic acid esters such as methyl chloroformate, ethylchloroformate, propyl chloroformate, isopropyl chloroformate, butylchloroformate, allyl chloroformate, phenyl chloroformate, nitrophenylchloroformate and benzyl chloroformate; and carbamic acid halides suchas N,N-dimethylcarbamyl chloride; among these chloroformic acid estersare preferred.

The amount of carbonylating agent VII may be used within a range ofpreferably 0.5 to 20 mol, and more preferably 1.1 to 10 mol, based onone mole of the imine derivative VI.

Examples of nitriles VIII include alkylsulfonylcyanides such asmethanesulfonylcyanide, ethanesulfonylcyanide, propanesulfonylcyanide,butanesulfonylcyanide, tert-butanesulfonylcyanide, anddodecanesulfonylcyanide; arylsulfonylcyanides such asbenzenesulfonylcyanide, toluenesulfonylcyanide,chlorobenzenesulfonylcyanide, nitrobenzenesulfonylcyanide andnaphthalenesulfonylcyanide; aralkylsulfonylcyanides such asbenzylsulfonylcyanide and nitrobenzylsulfonylcyanide; cyanoformic acidesters such as methyl cyanoformate, ethyl cyanoformate, propylcyanoformate, isopropyl cyanoformate, butyl cyanoformate, allylcyanoformate, phenyl cyanoformate, nitrophenyl cyanoformate and benzylcyanoformate. The amount of nitrile VIII may be used within a range ofpreferably 0.5 to 20 mol, and more preferably 1.1 to 10 mol, based onone mole of the imine derivative VI.

The reaction can be carried out in the presence or absence of a solvent.The solvent is not particularly limited, provided that the reaction isnot adversely affected, examples of which include aromatic hydrocarbonssuch as benzene, toluene, xylene, mesitylene and chlorobenzene; etherssuch as tetrahydrofuran and dioxane; amides such as dimethyl formamideand 1-methyl-2-pyrrolidinone; and dimethyl sulfoxide. The amount of thesolvent is not particularly limited, although it is usually used withina rage of preferably 1 to 200 times by weight based on the iminederivative VI.

The reaction temperature may vary, depending on the solvent, thecarbonylating agent VII, and the nitrile VIII that is used, but ispreferably within a range of 40° C. to the reflux temperature of thereaction system. The reaction can be carried out in a pressurized orreduced pressure state. The reaction time may vary, depending on thereaction temperature, but is usually rages from 30 minutes to 24 hours.The reaction time can be controlled by properly controlling the reactiontemperature.

The reaction is carried out in the following manner, for example. Thatis, the carbonylating agent VII is added dropwise to a mixed solution ofthe nitrile VIII and the imine derivative VI within a temperature rangefrom under ice cooling to the refluxing temperature of the reactionmixture, and after the completion of addition, the mixture is heated tothe desired temperature until the imine derivative VI disappears.

The resulting pyridine derivative I is isolated and purified from thereaction mixture in the usual manner which commonly used in theisolation and purification of organic compounds. For example, aftercooling the reaction mixture to room temperature, it is washed withsodium bicarbonate aqueous solution and saline water. Then, the solventis distilled off, and the residue is purified by recrystallization,chromatography, or the like. When the product is precipitated from thereaction mixture, the reaction mixture can be cooled and then filteredwith the addition of a poor solvent if necessary.

Step (c): Step for producing a pyridine carbonyl derivative II byreacting a pyridine ester derivative I-1 with a reducing agent, analkylating agent, an alkenylating agent, an arylating agent or anaralkylating agent.

Examples of reducing agents include metal borohydrides such as sodiumborohydride and lithium borohydride; and metal aluminum hydrides such asdiisobutyl aluminum hydride, lithium aluminum hydride and sodiumbismethoxyethoxyaluminum hydride. Examples of alkylating agents includealkyl metal compounds such as methyllithium, n-butyllithium,methylmagnesium chloride, methylmagnesium bromide, ethylmagnesiumchloride and methylcerium chloride; examples of alkenylating agentsinclude alkenyl metal compounds such as vinyllithium, vinylmagnesiumchloride, allyllithium and allylmagnesium chloride; examples ofarylating agents include aryl metal compounds such as phenyllithium andphenylmagnesium bromide; and examples of aralkylating agents includearalkyl metal compounds such as benzyllithium and benzyl-magnesiumbromide. The amount of reducing agent, the alkylating agent, thealkenylating agent, the arylating agent or the aralkylating agent may beused within a range of preferably 0.5 to 20 mol, and more preferably 1.1to 2.0 mol, based on one mole of the pyridine ester derivative I-1.

The reaction can be carried out in the presence or absence of a solvent.The solvent is not particularly limited, provided that the reaction isnot adversely affected, examples of which include ethers such as diethylether, diisopropyl ether, dibutyl ether, tetrahydrofuran,1,2-diethoxyethane and diethylene glycol dimethyl ether; hydrocarbonssuch as hexane, benzene, toluene, xylene, mesitylene, and chlorobenzene;and amides such as 1-methyl-2-pyrrolidinone. The amount of solvent isnot particularly limited, although it is usually used within a range ofpreferably 1 to 200 times by weight based on the pyridine esterderivative I-1.

The reaction temperature may vary, depending on the solvent, thereducing agent, the alkylating agent, the alkenylating agent, thearylating agent or the aralkylating agent that is used, but atemperature is usually preferred within a range of −100° C. to therefluxing temperature of the solvent. The reaction can be carried out ina pressurized or reduced pressure state. The reaction time also mayvary, depending on the reaction temperature, but is usually range from30 minutes to 24 hours. The reaction time can be controlled by properlycontrolling of the reaction temperature.

The resulting pyridine carbonyl derivative II is isolated and purifiedfrom the reaction mixture in the usual manner which commonly used in theisolation and purification of organic compounds. For example, afterreturning the reaction mixture to room temperature, it is then added toan acidic aqueous solution such as aqueous ammonium chloride and ishydrolyzed, it is then extracted with an organic solvent such as diethylether or ethyl acetate, the extract is washed with sodium bicarbonateaqueous solution and saline water, the solvent is distilled off, and theresidue is purified by distillation, recrystallization, chromatography,or the like.

A pyridine alcohol derivative III in which R⁵ and R⁶ are a hydrogen atomcan be obtained in a single stage when using a reducing agent withhydrogen as a nucleophilic agent, metal borohydrides such as sodiumborohydride, lithium borohydride; and metal aluminum hydrides such aslithium aluminum hydride, sodium bismethoxyethoxyaluminum hydride.

Step (d): Step for producing a pyridine alcohol derivative III byreacting a pyridine carbonyl derivative II with a reducing agent, analkylating agent, an alkenylating agent, an arylating agent or anaralkylating agent.

Examples of reducing agents include metal borohydrides such as sodiumborohydride and lithium borohydride and metal aluminum hydrides such asdiisobutyl aluminum hydride, lithium aluminum hydride, and sodiumbismethoxyethoxyaluminum hydride. Reduction can also be carried out theuse of hydrogen in the presence of a metal catalyst such as Raney nickelor Raney cobalt. Reduction by aluminum isopropoxide in isopropanol canalso be adopted. The amount of the reducing agent may be used preferablywithin a range of 1.0 to 20 mol, and preferably 1.1 to 5 mol, based onone mole of the pyridine carbonyl derivative II.

Examples of alkylating agents include alkyl metal compounds such asmethyllithium, n-butyllithium, methyl-magnesium chloride,methylmagnesium bromide, ethylmagnesium chloride, and methylceriumchloride; examples of alkenylating agents include alkenyl metalcompounds such as vinyllithium, vinylmagnesium chloride, allyllithium,and allylmagnesium chloride; examples of arylating agents include arylmetal compounds such as phenyllithium and phenylmagnesium bromide; andexamples of aralkylating agents include aralkyl metal compounds such asbenzyllithium and benzylmagnesium bromide. The amount of alkylatingagent, the alkenylating agent, the arylating agent or the aralkylatingagent may be used within a range of preferably 0.5 to 20 mol, and morepreferably 1.1 to 2.0 mol, based on one mole of the pyridine carbonylderivative II.

The reaction can be carried out in the presence or absence of a solvent.The solvent is not particularly limited, provided that the reaction isnot adversely affected, examples of which include alcohols such asmethanol, ethanol, propanol and isopropanol; ethers such as diethylether, diisopropyl ether, dibutyl ether, tetrahydrofuran,1,2-diethoxyethane and diethylene glycol dimethyl ether; andhydrocarbons such as hexane, heptane, cyclohexane, benzene, toluene, andxylene. The amount of solvent is not particularly limited, although itis preferably used within a range of 1 to 200 times by weight based onthe pyridine carbonyl derivative II.

The reaction temperature may vary, depending on the solvent, thereducing agent, the alkylating agent, the alkenylating agent, thearylating agent or the aralkylating agent that is used, but atemperature is preferred within a range of −100° C. to the refluxingtemperature of the solvent. The reaction can be carried out in apressurized or reduced pressure state. The reaction time also may vary,depending on the reaction temperature, but is usually range from 30minutes to 24 hours. The reaction time can be controlled by properlycontrolling of the reaction temperature.

The resulting pyridine alcohol derivative III is isolated and purifiedfrom the reaction mixture in the usual manner which commonly used in theisolation and purification of organic compounds. For example, afterreturning the reaction mixture to room temperature, the reaction mixtureis then added to an acidic aqueous solution such as aqueous ammoniumchloride and is hydrolyzed, it is then extracted with an organic solventsuch as diethyl ether or ethyl acetate, the extract is washed withsodium bicarbonate aqueous solution and saline water, the solvent isdistilled off, and the residue is purified by distillation,recrystallization, chromatography, or the like.

Step (e): Step for producing a pyridine β-ketoester derivative V byreacting a pyridine ester derivative I-1 with an ester compound IV inthe presence of a base.

Examples of bases include alkali metals such as sodium, lithium, andpotassium; alkaline earth metals such as calcium; metal alcoholates suchas sodium methoxide, sodium ethoxide, sodium propoxide, sodiumisopropoxide, sodium butoxide, sodium tert-butoxide, sodium benzyloxide,potassium methoxide, potassium ethoxide, potassium propoxide, potassiumisopropoxide, potassium butoxide and potassium tert-butoxide; organicmagnesium halides such as methylmagnesium bromide, ethylmagnesiumbromide, isopropylmagnesium bromide, and mesitylmagnesium bromide; metalhydrides such as sodium hydride and potassium hydride; and metal amidessuch as sodium amide, potassium amide, and lithium diisopropylamide. Theamount of base is preferably used within a range of 0.5 to 10 mol, andmore preferably 1 to 3 mol, based on one mole of the pyridine esterderivative I-1.

The ester compound IV is an ester compound derived from a carboxylicacid having a hydrogen atom in the alpha position, preferably an estercompound, such as a methyl ester, ethyl ester, propyl ester, isopropylester, butyl ester, isobutyl ester, 2-methylpropyl ester, tert-butylester, phenyl ester, benzyl ester, or chlorophenyl ester of a carboxylicacid such as acetic acid, propionic acid, butyric acid, isobutyric acid,2-methylpropionic acid, valeric acid, isovaleric acid, caproic acid, orphenylacetic acid. Among these, aliphatic lower alcohol esters such asmethyl esters, ethyl esters, propyl esters, isopropyl esters, butylesters, isobutyl esters, 2-methylpropyl esters and tert-butyl esters arepreferred.

The amount of ester compound IV is used preferably within a range of 0.5to 10 mol, and more preferably 1 to 3 mol, based on one mole of thepyridine ester derivative I-1.

Although the reaction in this step can be carried out in the absence ofa solvent, it is preferably carried out in the presence of a solvent.

Solvents are not particularly limited, provided that the reaction is notadversely affected, examples of which include aliphatic hydrocarbonssuch as pentane, hexane, cyclohexane, octane and ligroin; aromatichydrocarbons such as benzene, toluene, xylene, cumene and mesitylene;ethers such as diethyl ether, tetrahydrofuran, and dioxane; polyetherssuch as ethylene glycol dimethyl ether, diethylene glycol dimethylether, triethylene glycol dimethyl ether, tetraethylene glycol dimethylether, ethylene glycol diethyl ether, diethylene glycol diethyl ether,triethylene glycol diethyl ether and tetraethylene glycol diethyl ether;and alcohols such as methanol, ethanol, propanol, isopropanol, butanoland t-butanol. Among these, the use of aromatic hydrocarbons, ethers,and polyethers as the solvent is preferred in view of the reaction rate,solubility of the pyridine derivative I, and the like. The amount ofsolvent is not particularly limited, provided that it is an amountallowing the pyridine ester derivative I-1 to dissolve under thereaction conditions, although it is preferably used within a range of0.5 to 1000 times by weight, and more preferably 0.5 to 100 times byweight, based on the pyridine ester derivative I-1.

The reaction temperature is preferably within a range of 0 to 200° C.,and more preferably 10 to 150° C.

The reaction in this step is not limited to any particular method,examples of which include: (1) mixing the prescribed amounts of thepyridine ester derivative I-1, the base, the ester compound IV and asolvent, and allowing the mixture to react at the prescribedtemperature; (2) dissolving the prescribed amount of the pyridine esterderivative I-1 in a solvent, adding the base to the solution, heatingthe solution to the desired temperature, and then adding the estercompound IV all at once, intermittently or continuously, either as suchor dissolved in a solvent; and (3) dissolving the prescribed amount ofthe base in the solvent, adding the ester compound IV to the solution,heating the solution to the desired temperature, and then adding thepyridine ester derivative I-1 all at once, intermittently, orcontinuously, either as such or dissolved in a solvent, to bring aboutthe reaction.

The resulting pyridine β-ketoester derivative V can be readily isolatedby neutralizing the reaction solution with the addition of an equivalentamount of acid relative to the base that was used, by then extractingthe product with methylene chloride, toluene, xylene, benzene,chloroform, pentane, hexane, heptane or the like, and by concentratingthe extract. Examples of acids which can be used for such purposesinclude carboxylic acids such as acetic acid and formic acid, andinorganic acids such as hydrochloric acid and sulfuric acid. The purityof the product can be increased by recrystallization, if necessary.

Under these reaction conditions, depending on the combination of thepyridine ester derivative I-1, the base, and the ester compound IV, aswell as the proportions in which they are used, especially when using ametal alcoholate as the base or when using an alcohol as the solvent, atransesterification reaction sometimes progresses between the grouprepresented by -X in the pyridine ester derivative I-1,the grouprepresented by —OR³ in the ester compound IV, the alcoholate moiety ofthe metal alcoholate and the alcohol. In such cases, the product canbecome a mixture of various types of moieties represented by —OR⁴ in thepyridine β-ketoester derivative V, but the purity of such mixtures canbe readily increased by common separation and purification means such asdistillation, column chromatography, and recrystallization. Thesemixtures may also be used without any problems in the next step (f) forobtaining the pyridine carbonyl derivative II.

Step (f): Step for producing a pyridine carbonyl derivative II byhydrolysis and decarboxylation of a pyridine β-ketoester derivative V.

The amount of water that is used for hydrolysis is not. particularlylimited, although the use of at least one mole based on one mole of thepyridine β-ketoester derivative V is preferred in view of obtaining thetarget pyridine carbonyl derivative II with good yields, and no morethan 100 mol water based on one mole of the pyridine β-ketoesterderivative V is usually preferred in view of the reaction rate, theextraction efficiency following the reaction, the volume efficiency ofthe equipment, and the like.

Any common acid or base used in the hydrolysis of esters can be used inthe hydrolysis reaction. Examples of acids include inorganic acids suchas hydrochloric acid and sulfuric acid, and acidic gases such ashydrogen chloride gas can also be used. Examples of bases include alkalimetal hydroxides such as sodium hydroxide and potassium hydroxide.

The intermediate product obtained by the hydrolysis of the pyridineβ-ketoester derivative V is unstable under these reaction conditions,and the pyridine carbonyl derivative II is produced as a result of therapid progress of the decarboxylation, thus allowing the decarboxylationto be carried out, usually at the same time as the hydrolysis, in thesame reactor using the unmodified acid or base used in the hydrolysis.More acid or base can be added during the reaction to promote thehydrolysis and decarboxylation. The type of acid or base that is addedat such times may be the same as, or different from, the acid or baseinitially used in the hydrolysis and decarboxylation. The amount of acidor base may be used within a range of preferably 0.001 to 100 mol, andmore preferably 0.01 to 10 mol, based on one mole of the pyridineβ-ketoester derivative V.

Methods for carrying out the reaction include methods in which thehydrolysis and decarboxylation are first started under basic conditions,and excess acid is added to the reaction system midway during thereaction to bring about acidic conditions, and methods in which thehydrolysis and decarboxylation are first started under acidicconditions, and excess base is added to the reaction system midwayduring the reaction to bring about basic conditions.

To obtain the pyridine carbonyl derivative II, a reaction mixturecontaining the pyridine β-ketoester derivative V is obtained by means ofthe reaction in step (e), and water and an acid or base are then addedto the reaction solution without separating the pyridine β-ketoesterderivative V from the reaction mixture to carry out the hydrolysis anddecarboxylation in step (f), allowing the pyridine carbonyl derivativeII to be obtained.

When the hydrolysis and decarboxylation in step (f) are then carried outwithout isolating the pyridine β-ketoester derivative V from thereaction mixture obtained in the reaction in step (e), the pyridineβ-ketoester derivative V contained in the reaction mixture is quantifiedand analyzed, and the acid or base is used in an amount within the rangedescribed above relative to that amount. The amount of acid or base maybe used within a range of preferably 0.001 to 100 mol, and morepreferably 0.01 to 10 mol, based on one mole of the pyridine esterderivative I-1 used in step (e). The amount of water is used within arange of preferably 1 to 100 mol based on the amount of the pyridineβ-ketoester derivative V contained in the reaction mixture. Water mayalso be used within a range of preferably 1 to 100 mol based on one moleof the pyridine ester derivative I-1.

Because a base is already present in the reaction mixture containing thepyridine β-ketoester derivative V obtained in step (e), the addition ofwater allows the existing base to act as a promoter in the hydrolysisand decarboxylation. In this embodiment, the neutralization in step (e)can be omitted.

The hydrolysis and decarboxylation may be carried out in the presence ofan organic solvent. The type of organic solvent is not particularlylimited, provided that the reaction is not adversely affected, examplesof which include aliphatic hydrocarbons such as pentane, hexane,cyclohexane, octane and ligroin; aromatic hydrocarbons such as benzene,toluene, xylene, cumene and mesitylene; ethers such as diethyl ether,tetrahydrofuran and dioxane; polyethers such as ethylene glycol dimethylether, diethylene glycol dimethyl ether, triethylene glycol dimethylether, tetraethylene glycol dimethyl ether, ethylene glycol diethylether, diethylene glycol diethyl ether, triethylene glycol diethyl etherand tetraethylene glycol diethyl ether; and alcohols such as methanol,ethanol, propanol, isopropanol, butanol and t-butanol. Among these, theuse of aromatic hydrocarbons, ethers and polyethers is preferred in viewof the reaction rate, solubility of the pyridine β-ketoester derivativeV, and the like. The amount of solvent is not particularly limited,although it is preferably used within a range of 0.5 to 100 weight partsbased on the pyridine β-ketoester derivative V or the pyridine esterderivative I-1.

When the hydrolysis and decarboxylation in step (f) are then carried outwithout isolating the pyridine β-ketoester derivative V from thereaction mixture obtained in the reaction in step (e), the solvent usedin step (e) can be used as such in step (f).

The reaction temperature is preferably within a range of 0 to 200° C.,and more preferably 10 to 150° C.

The resulting pyridine carbonyl derivative II is isolated and purifiedfrom the reaction mixture in the usual manner which commonly used in theisolation and purification of organic compounds. For example, aftercooling the reaction mixture to room temperature, it is extracted withan organic solvent such as methylene chloride, toluene, xylene, benzene,chloroform, pentane, hexane or heptane, the extract is washed withsaline water, the solvent is distilled off, and the residue is purifiedby distillation, recrystallization, chromatography, or the like.

The pyridine carbonyl derivative II thus obtained can be converted tothe corresponding pyridine alcohol derivative III by using theprocedures in step (d).

Of the pyridine derivative represented by the General Formula I-2contained the pyridine derivative I, for example,5-benzenesulfonylfuro[2,3-c]pyridine can be converted to theintermediate noted in International Unexamined Patent Application WO96/35678 by the following method, and a compound having antiviralactivity can be derived by the method noted in the same application.

That is, 5-benzenesulfonylfuro[2,3-c]pyridine is converted to5-cyanofuro[2,3-c]pyridine by reacting with an alkali metal cyanide. Thecyanation can be carried out with or without a solvent. The solvent isnot particularly limited, provided that the reaction is not adverselyaffected, examples of which include polar solvents such as dimethylformamide, dimethyl sulfoxide, 1,3-dimethyl-2-imidazolidione. Thisreaction can also be carried out as a two-phase reaction using anphase-transfer catalyst. The reaction is carried out by heating5-benzenesulfonylfuro[2,3-c]pyridine and an excess amount of an alkalimetal cyanide at a temperature within a range of room temperature to thereflux temperature. The resulting 5-cyanofuro[2,3-c]pyridine can beconverted to 5-acetylfuro [2,3-c]pyridine by reacting with a methylatingagent such as methyllithium or methylmagnesium chloride. The amount ofthe methylating agent is preferably within a range of 0.8 to 2 mol basedon the starting pyridine derivative.

5-Acetylfuro[2,3-c]pyridine can be synthesized by reacting an acetylanion equivalent with 5-benzenesulfonylfuro[2,3-c]pyridine, and thensubsequent deprotection. Conventional acetyl anion equivalents can beused as the acetyl anion . equivalent, although preferred examplesinclude lactonitrile cyanhydrin ether, and acetyl anion equivalentsprepared from an acetaldehyde thioacetal, thioacetal monoxide or thelike and a strong base such as butyllithium, tert-butyllithium,methyllithium, phenyllithium, lithium diisopropylamide, lithiumhexamethyldisilazide or sodium hexamethyldisilazide. The acetyl anionequivalent is preferably used in an amount of 0.8 to 2 mol based on onemole of the starting pyridine derivative.

The reaction may be carried out in a solvent that does not adverselyaffect the reaction, examples of such solvents preferably includingethers such as diethyl ether, tetrahydrofuran, dimethoxyethane anddioxane. The reaction temperature is preferably within the range of −40°C. to 100° C.

The resulting product is subsequently treated and deprotected by acommon method, and the resulting 5-acetylfuro[2,3-c]pyridine can beconverted to the intermediate by reduction with sodium borohydride,diisobutyl aluminum hydride, lithium aluminum hydride or the like notedin International Unexamined Patent Application WO 96/35678.

EXAMPLES

The present invention is described in further detail below withreference to examples, but the present invention is not limited in anyway by these examples.

Example 1

3-Methylfuran-2-carbaldehyde (14.8 g, 0.135 mol) was mixed with hexane(50 mL), aniline (15.1 g, 0.162 mol) was added over 30 minutes at roomtemperature, and the mixture was heated to reflux for 4 hours withstirrng. The mixture was allowed to cool to room temperature, and thesolvent was then distilled off to give 28.1 g of the crude product of3-methylfuran-2-carbaldehyde-N-phenylimine.

Benzenesulfonyl cyanide (90.2 g, 0.540 mol) and ethyl chloroformate(29.3 g, 0.270 mol) were mixed at room temperature in xylene (125 mL)and were stirred to reflux at a temperature of 120 to 140° C. A xylene(75 mL) solution of the crude 3-methylfuran-2-carbaldehyde-N-phenylimine(28.1 g) obtained above was added dropwise over 2 hours to the mixture.After all the solution had 20 been added, the reaction mixture washeated to reflux for 3 hours, it was then cooled to room temperature,and the solvent was distilled off to give 81.3 g of crude product.

This product was purified by column chromatography on silica gel, giving17.2 g of 5-benzenesulfonylfuro[2,3-c]pyridine.

¹H-NMR spectra (270 MHz, CDCl₃, TMS, ppm) δ: 6.99 (1H, dd, J=2.16 Hz,0.81 Hz), 7.49 to 7.62 (3H, m), 7.91 (1H, d, J=2.16 Hz), 8.07 to 8.11(2H, m), 8.56 (1H, d, J=0.81 Hz), 8.90 (1H, s).

As is apparent from Example 1, the present invention can provide amethod by which pyridine derivatives that are useful as intermediatesfor antiviral agents and the like can be produced with good yields in anindustrially useful manner under moderate conditions.

Example 2

Ethyl cyanoformate(21.4 g, 0.216 mol) and3-methylfuran-2-carbaldehyde-N-phenylimine(10.0 g, 54.1 mmol) were mixedat room temperature in xylene (50 mL) then heated to reflux at 120 to140° C. with stirring. A xylene (30 mL) solution of 11.7 g (0.108 mol)of ethyl chloroformate was added dropwise for an hour to the resultingmixture. After all the solution had been added, the reaction mixture washeated to reflux for 2 hours, it was allowed to cool to roomtemperature, and the solvent was distilled off to give 14.0 g of crudeproduct. This product was purified by column chromatography on silicagel, giving 5.40 g (52.3% yield) of 5-ethoxycarbonylfuro[2,3-c]pyridine.

¹H-NMR spectra (270 MHz, CDCl₃, TMS, ppm) δ: 1.47 (3H, t, J=7.16 Hz),4.51 (2H, q, J=7.16 Hz), 6.94 (1H, dd, J=2.70 Hz, 1.08 Hz), 7.85 (1H, d,J=2.70 Hz), 8.50 (1H, d, J=1.08 Hz), 8.99 (1H, s).

Example 3

n-Butyl cyanoformate(13.7 g, 0.108 mol) and3-methylfuran-2-carbaldehyde-N-phenylimine(5.0 g, 27.0 mmol) were mixedat room temperature in xylene (25 mL) then heated to reflux at 120 to140° C. with stirring. A xylene (15 mL) solution of 7.40 g (54.2 mol) ofn-butyl chloroformate was added dropwise for an hour to the resultingmixture. After all the solution had been added, the reaction mixture washeated to reflux for 2 hours, it was allowed to cool to roomtemperature, and the solvent was distilled off to give 7.10 g of crudeproduct. This product was purified by column chromatography on silicagel, giving 2.71 g (45.8% yield) of5-n-butoxycarbonylfuro[2,3-c]pyridine.

¹H-NMR spectra (270 MHz, CDCl₃, TMS, ppm) δ: 0.99 (3H, t, J=7.43 Hz),1.49 (2H, tq, J=7.43 Hz), 1.84 (2H, tt, =7.43 Hz), 4.45 (2H, t, J=7.43Hz), 6.94 (1H, dd, J=2.43 Hz, J=0.81 Hz), 7.85 (1H, d, J=2.43 Hz), 8.48(1H, d, J=0.81 Hz), 8.99 (1H, s).

Example 4

5-Ethoxycarbonylfuro[2,3-c]pyridine obtained in Example 2(3.82 g, 20.0mmol) was dissolved in tetrahydrofuran (50 mL) and cooled to −30° C. Tothe cooled solution, 22.0 mL (22.0 mol) of 1.0 M solution ofmethyllithium/diethyl ether was added, and the solution was stirred for2 hours at the same temperature, the reaction mixture was then pouredinto 100 mL of 5% ammonium chloride aqueous solution which had beencooled on ice, and the product was extracted twice with 100 mL of ethylacetate. After washing with 100 mL of saturated sodium bicarbonateaqueous solution and 100 mL of saturated saline water, the extract wasconcentrated to give 3.12 g of crude product. This product was purifiedby column chromatography on silica gel, giving 2.48 g (77.0% yield) of5-acetylfuro[2,3-c]pyridine.

¹H-NMR spectra (270 MHz, CDCl₃, TMS, ppm) δ: 2.79 (3H, s), 6.94 (1, dd,J=2.16 Hz, J=1.08 Hz), 7.83 (1H, d, J=2.16 Hz), 8.39 (1H, d, J=1.08 Hz),8.91 (1H, s).

Example 5

5-Acetylfuro[2,3-c]pyridine obtained in Example 4(2.42 g, 15.0 mmol) wasdissolved in toluene (30 mL), and the solution was cooled to 0° C. Tothe cooled solution,16.0 mL (16.0 mmol) of 1.0 M solution of diisobutylaluminum hydride in toluene solution was added, and the solution wasstirred for 2 hours at the same temperature, the reaction mixture wasthen poured into 100 mL of a 5% ammonium chloride aqueous solution whichhad been cooled on ice, and it was extracted twice with 100 mL of ethylacetate. After washing with 100 mL of saturated sodium bicarbonateaqueous solution and 100 mL of saturated saline water, the extract wasconcentrated to give 2.36 g of crude product. This product was purifiedby column chromatography on silica gel, giving 2.25 g (92.0% yield) of5-(1-hydroxyethyl)furo [2,3-c]pyridine.

As is apparent from Examples 2 to 5, the present invention can provide amethod by which pyridine alcohol derivatives that are useful asintermediates for antiviral agents and the like can be produced withgood yields in an industrially useful manner under moderate conditions.It also provides synthetic intermediates and a method of producing themgiving such the method.

Example 6

5-Ethoxycarbonylfuro[2,3-c]pyridine obtained in Example 2(956 mg, 5.0mmol) was dissolved in 10 mL of toluene, 2.55 g (7.5 mmol) of a 20%ethanol solution of sodium ethoxide was added dropwise at roomtemperature to the solution, and 661 mg (7.5 mmol) of ethyl acetate wasthen added dropwise at room temperature with stirring. After all theethyl acetate had been added, the reaction mixture was heated to 80° C.,and a reaction was carried out for 8 hours. The reaction solution wasthen cooled to 5° C. and was neutralized with 450 mg (7.5 mmol) ofacetic acid as the temperature was held 5-10° C., the solution wasstirred for 30 minutes as the temperature was maintained, 1 mL of waterwas added, and the solution was returned to room temperature. Theorganic layer was separated, the aqueous layer was extracted twice with5 mL of methylene chloride, and the combined organic layer was driedwith anhydrous magnesium sulfate and then concentrated in a rotaryevaporator to give 851 mg of solids. This solids were recrystallizedfrom a mixed solvent of toluene-hexane, giving 769 mg (66% yield) ofethyl β-oxo-5-furo[2,3-c]pyridinepropionate in a purity of 99% by HPLC.

¹H-NMR spectra (270 MHz, CDCl₃, TMS, ppm) δ: 1.25 (3H, t, J=7.17 Hz),4.21 (2H, q, J=7.17 Hz), 4.25 (2H, s), 6.95 (1H, d, J=2.46 Hz), 7.85(1H, d, J=1.97 Hz), 8.42 (1, s), 8.88 (1H, s).

Example 7

5-Ethoxycarbonylfuro[2,3-c]pyridine(956 mg, 5.0 mmol) was dissolved in10 mL of toluene, 510 mg (7.5 mmol) of sodium ethoxide was added at roomtemperature to the solution, and 661 mg (7.5 mmol) of ethyl acetate wasthen added dropwise at room temperature with stirring. After all theethyl acetate had been added, the reaction mixture was heated to 80° C.,and a reaction was carried out for 4 hours. The reaction solution wasthen cooled to 5° C. and was neutralized with 450 mg (7.5 mmol) ofacetic acid as the temperature was held 5-10° C., the solution wasstirred for 30 minutes as the temperature was maintained, 1 mL water wasthen added, and the solution was returned to room temperature. Theorganic layer was separated, the aqueous layer was extracted twice with5 mL of methylene chloride, and the combined organic layer was driedwith anhydrous magnesium sulfate and then concentrated in a rotaryevaporator, and the resulting solids were recrystallized from a mixedsolvent of toluene-hexane, giving 840 mg (72% yield) of ethylβ-oxo-5-furo[2,3-c]pyridinepropionate in a purity of 99% by HPLC.

Example 8

As 510 mg (7.5 mmol) of sodium ethoxide was stirred in 5 mL toluene,1.16 g (10.0 mmol) of t-butyl acetate was added dropwise at roomtemperature to the solution. Then, 956 mg (5.0 mmol) of5-ethoxycarbonylfuro[2,3-c]pyridine dissolved in 5 mL of toluene wasadded dropwise at room temperature to the above solution. After all thesolution had been added, the reaction mixture was heated to 60° C., anda reaction was carried out for 3 hours. The reaction solution was thencooled to 5° C. and was neutralized with 450 mg (7.5 mmol) of aceticacid as the temperature was held 5-10° C., the solution was stirred for30 minutes as the temperature was maintained, 1 mL water was then added,and the solution was returned to room temperature. The organic layer wasseparated, the aqueous layer was extracted twice with 5 mL of methylenechloride, and the combined organic layer was dried with anhydrousmagnesium sulfate and then concentrated in a rotary evaporator. Theresulting solids were recrystallized from a mixed solvent oftoluene-hexane mixture, giving 933 mg (80% yield) of ethylβ-oxo-5-furo[2,3-c]pyridinepropionate in a purity of 99% by HPLC.

Example 9

As 405 mg (7.5 mmol) of sodium methoxide was stirred in 5 mL toluene,1.16 g (10.0 mmol) of t-butyl acetate was added dropwise at roomtemperature to the solution. Then, 956 mg (5.0 mmol) of5-ethoxycarbonylfuro[2,3-c]pyridine was dissolved in 5 mL of toluene wasadded dropwise at room temperature to the above solution. After all thesolution had been added, the reaction mixture was heated to 60° C., anda reaction was carried out for 3 hours. The reaction solution was thencooled to 5° C. and was neutralized with 450 mg (7.5 mmol) of aceticacid as the temperature was held 5-10° C., the solution was stirred for30 minutes as the temperature was maintained, 1 mL water was then added,and the solution was returned to room temperature. The organic layer wasseparated, the aqueous layer was extracted twice with 5 mL of methylenechloride, and the combined organic layer was dried with anhydrousmagnesium sulfate and then concentrated in a rotary evaporator to give971 mg solids. NMR analysis revealed those to be a mixture of methylβ-oxo-5-furo[2,3-c]pyridinepropionate, ethyl β-oxo-5-furo[2,3-c]pyridinepropionate, and

tert-butyl β-oxo-5-furo[2,3-c]pyridinepropionate (molar ratio of55:44:1). The NMR spectra for the aforementioned ethylβ-oxo-5-furo[2,3-c]pyridinepropionate were consistent with those of theethyl β-oxo-5-furo[2,3-c]pyridinepropionate obtained in Example 6.

Methyl β-oxo-5-furo[2,3-c]pyridinepropionate

¹H-NMR spectra (270 MHz, CDCl₃, TMS, ppm) δ: 3.75 (3H, s), 4.29 (2H, s),6.95 (1H, d, J=1.97 Hz), 7.85 (1H, d, J=1.98 Hz), 8.39 (1H, s), 8.88(1H, s).

tert-Butyl β-oxo-5-furo[2,3-c]pyridinepropionate

¹H-NMR spectra (270 MHz, CDCl₃, TMS, ppm) δ: 1.42 (9H, s), 4.13 (2H, s),6.94 (1H, d, J=1.98 Hz), 7.83 (1H, d, J=1.98 Hz), 8.40 (1H, s), 8.88(1H, s).

Example 10

The 971 mg of the mixture of methylβ-oxo-5-furo[2,3-c]pyridinepropionate, ethylβ-oxo-5-furo[2,3-c]pyridinepropionate, and tert-butylβ-oxo-5-furo[2,3-c]pyridinepropionate (molar ratio of 55:44:1) obtainedin Example 9 was dissolved in 20 mL of toluene, and 1.04 g of 35%hydrochloric acid was added at room temperature with stirring. Afteraddition, the reaction mixture was heated to 60° C., and a reaction wascarried out for 3 hours with stirring. The reaction solution was thencooled to room temperature and was neutralized with 8.40 g of 5% sodiumhydroxide aqueous solution. The organic layer was separated, the aqueouslayer was extracted twice with 5 mL of methylene chloride, and thecombined organic layer was dried with anhydrous magnesium sulfate andthen concentrated in a rotary evaporator. The resulting solids wererecrystallized from a mixed solvent of toluene-hexane, giving 629 mg of5-acetylfuro[2,3-c]pyridine in a purity of 99% by HPLC (78% yield from5-ethoxycarbonylfuro [2,3-c]pyridine).

Example 11

Ethyl β-oxo-5-furo[2,3-c]pyridinepropionate(1.17 g, 15 5.0 mmol) wasdissolved in 20 mL of toluene, and 1.5 mL (7.5 mmol) of 10 N sulfuricacid was added at room temperature with stirring. After addition, thereaction mixture was heated to 80° C., and a reaction was carried outfor 6 hours with stirring. The solution was then cooled to roomtemperature and neutralized with 12 mL of 5% sodium hydroxide aqueoussolution. The organic layer was separated, the aqueous layer wasextracted twice with 5 mL of methylene chloride, and the combinedorganic layer was dried with anhydrous magnesium sulfate and thenconcentrated in a rotary evaporator. The resulting solids wererecrystallized from a mixed solvent of toluene-hexane, giving 580 mg of5-acetylfuro[2,3-c]pyridine in a purity of 99% by HPLC (72% yield).

Example 12

Ethyl β-oxo-5-furo[2,3-c]pyridinepropionate (583 mg, 2.5 mmol) obtainedin Example 7 was dissolved in 10 mL of toluene, and 3 of 10% sodiumhydroxide aqueous solution was added with stirring. After addition, thereaction mixture was heated to 60° C., and a reaction was carried outfor 8 hours with stirring. It was then cooled to room temperature, theorganic layer was separated, the aqueous layer was extracted twice with5 mL of methylene chloride, and the combined organic layer was driedwith anhydrous magnesium sulfate and then concentrated in a rotaryevaporator. The resulting solids were recrystallized from a mixedsolvent of toluene-hexane, giving 205 mg (51% yield) of5-acetylfuro[2,3-c]pyridine in a purity of 99% by HPLC.

Example 13

As 405 mg (7.5 mmol) of sodium methoxide was stirred in 5 mL of toluene,1.16 g (10.0 mmol) of tert-butyl acetate was added dropewise at roomtemperature to the solution. Then, 956 mg (5.0 mmol) of5-ethoxycarbonylfuro[2,3-c]pyridine dissolved in 5 mL of toluene wasadded dropwise at room temperature to the above solution. After all thesolution had been added, the reaction mixture was heated to 60° C., areaction was carried out for 3 hours. The resulting reaction mixture wasthen neutralized with 450 mg (7.5 mmol) of acetic acid, the solution wasstirred for 30 minutes, 1.5 mL (7.5 mmol) of 5 N hydrochloric acid wasthen added, and the solution was stirred for 5 hours at 60° C. to carryout a reaction. The solution was then returned to room temperature, theorganic layer was separated, the aqueous layer was extracted twice with5 mL of methylene chloride, and the combined organic layer was driedwith anhydrous magnesium sulfate and then concentrated in a rotaryevaporator. The resulting solids were recrystallized from a mixedsolvent of toluene-hexane, giving 580 mg (72% yield) of5-acetylfuro[2,3-c]pyridine in a purity of 99% by HPLC.

Example 14

5-Acetylfuro[2,3-c]pyridine (2.42 g, 15.0 mmol) obtained by the methodin Example 13 was dissolved in toluene (30 mL), and the solution wascooled to 0° C. To the cooled solution, 16.0 mL (16.0 mmol) of 1.0 Msolution of diisobutyl aluminum hydride in toluene was added, and thesolution was stirred for 2 hours at this temperature, the reactionmixture was then poured into 100 mL of a 5% ammonium chloride aqueoussolution which had been cooled on ice, and it was extracted twice with100 mL of ethyl acetate. The extract was washed with 100 mL of saturatedsodium bicarbonate aqueous solution and 100 mL of saturated salinewater, and the solvent was concentrated to give 2.36 g of crude product.This product was purified by column chromatography on silica gel, giving2.25 g (92.0% yield) of 5-(1-hydroxyethyl)furo[2,3-c]pyridine.

¹H-NMR spectra (270 MHz, CDCl₃,TMS, ppm) δ: 1.55 (3H, s), 4.03 (1H, s),4.99 (1H, q, J=5.93 Hz), 6.80 (1H, d, J=1.98 Hz), 7.53 (1H, s), 7.77(1H, d, J=2.47 Hz), 8.80 (1H, s).

As is apparent from Examples 6 to 14, the present invention can providemethods by which pyridine derivatives that are useful as intermediatesfor antiviral agents and the like can be produced with good yields in anindustrially useful manner under moderate conditions. It also providessynthetic intermediates and methods of producing them giving such themethods.

The entire disclosure of the specifications, claims and summaries ofJapanese Patent Applications No. 9-291075 filed on Oct. 23, 1997, No.10-64862 filed on Mar. 16, 1998 and No. 10-219943 filed Aug. 4, 1988 isherein incorporated by reference.

What is claimed is:
 1. A method for producing a pyridine derivativerepresented by general Formula I

where n of Z^(n) is 1 or 2; Z¹ represents —COX; X represents an alkoxylgroup, an alkenyloxy group, an aryloxy group or an aralkyloxy groupwhich may be substituted; Z² represents an organic sulfonyl grouprepresented by the formula, —SO₂R⁹; R⁹ is an organic group; and Arepresents a divalent organic group containing one to three oxygenatoms, nitrogen atoms and/or sulfur atoms, wherein A forms a 5-, 6-, 7-,or 8-membered ring together with two bonded carbon atoms, where saidring may form a condensed ring with one or more additional rings;wherein the method comprises: reacting an amine derivative representedby general Formula VI

where R⁷ is an alkyl group, an alkenyl group, an aryl group or anaralkyl group which may be substituted; and A is the same as above; witha carbonylating agent represented by general Formula VII

where R⁸ is a hydrogen atom, or an alkyl group, an alkenyl group, anaryl group, an aralkyl group, an alkoxyl group, an alkenyloxy group, anaryloxy group, an aralkyloxy group or an amino group which may besubstituted; and Y represents a leaving group; and a nitrile derivativerepresented by general Formula VIII Z^(n)CN  (VIII) where Z^(n) is thesame as above; to obtain the pyridine derivative represented by generalFormula I.
 2. A method according to claim 1, wherein said aminederivative represented by general Formula VI

where R⁷ is an alkyl group, an alkenyl group, an aryl group or anaralkyl group which may be substituted; and A represents a divalentorganic group containing one to three oxygen atoms, nitrogen atomsand/or sulfur atoms, wherein A forms a 5-, 6-, 7-, or 8-membered ringtogether with two bonded carbon atoms, where said ring may form acondensed ring with one or more additional rings; is obtained by amethod, comprising: reacting an aldehyde derivative represented bygeneral Formula IX

where A is the same as above; with a primary amine represented bygeneral Formula X R⁷NH₂  (X) where R⁷ is the same as above; to obtainthe imine derivative represented by general Formula VI.